Circuit interrupter



INVENTOR (XW/fz f//da/ ATTORNEY C. L. DENAULT CIRCUIT INTERRUPTER FiledMarch 29. 1934' Jan. 25, 1938.

Patented Jan.. 25, 1938 y CIRCUIT INTERRUPTER Clinton L. Denault, Forestlilll, Wilkimbnrg, Pa.,

assignor to Westinghouse Electric & Manufacturing Company, EastPittsburgh, Pa., a corporation of Pennsylvania Application March 29,1934, Serial No. 717,940

19 claims.; (C1. 20c-1z0) My invention relates to 'circuit interruptersand'Y particularly to high voltage circuit interrupters .of the typewhich utilizes an expulsive gas blast for extinguishing the arc formedincident to the interruption of the controlled circuit.

The commonest form of expulsion circuit interrupter is the well knownexpulsion fuse. This device usually comprises a tubular arc passage, ameans, such as a fuse, for establishing the arc within the tubular arcpassage, and a means for producing an expulsive gas blast which ilowslongitudinally through the arc to effect its extinguishment. Thesimplest method of producing this gas blast consists in the provision ofa lining for the arc passage which is formed of a material that iscapable of evolving considerable quantities of an are extinguishing gaswhen placed in proximity to an electric arc. The eiliciency and thereliability of operation of these devices depends to a great extent uponthe amount and the chemical characteristics of the gas which is. causedto expulsively flow through the arc during the circuit interruptingoperation, and one principal problem of the art has always d been thesecuring of an adequate volume of gas having a satisfactory chemicalcomposition.

The rate of evolution of gas from the surface of the lining of the arcpassage depends to a great extent upon the intimacy of contact betweenthe lining and the arc, and it is obvious that the maximum possibleevolution of gas (and the most efficient operation of the interrupter)will be effected when the arc completely fills the arc passage.Unfortunately, however, the magnitude of the overload current in mostpresent-day circuits varies through wide limits, and the physicaldimensions of the arc `likewise vary, in direct proportion. It mightappear that this would not create any serious diili'culties, since thearc pas- 40 sage could be made small enough to cause an intimateengagement between the lining and the surface of the smallest magnitudearc that might be drawn within that passage.

The problem is not so simply solved, because, while intimate engagementbetween the lining of the arcvpassage and the arc is imperative, it

55 may be sufliciently to become cenducting `danger of rupture orexcessive heating. vious result of this is that for most circuits theCOD- circuit interrupter, or failure ofJ the device to.

operate, during the occurrence of very heavy overload conditions makesit necessary that the physical dimensions of the arc passage shall besufficiently large to permit an arc having the largest possible .currentmagnitude considering the circuit with which the device is to be used,to be drawn within the arc passage without The obarc pasage must have avery considerable crosssectional area, and when the interrupter is inuse on such circuits, the low magnitude arcs produced by normaloverloads will but partially illl the arc passage. Under theseconditions, only a small volume of arc extinguishing gas will begenerated, and the eiliciency of the interrupter will be very low. Infact, if the current magnitude of the arc is very small, and thedimensions of the arc passage, even reasonably large, a small currentarc drawn therein may not be extinguished at all. i

To overcome this difficulty, and to assure efflcient operation o-f theinterrupter under varying conditions ofarc current, the prior artstructures have utilized two arc passages, one of large' cross-sectionalarea, wherein arcs of heavy current magnitudes are interrupted, and oneof small cross-sectional area wherein arcs of a lower current magnitudeare extinguished. Y This arrangement requires selective means forassuring that the are shall be drawn in the proper passage and is notentirely satisfactory from an economic viewpoint. A

TLhe principal object of my invention, therefore, is to provide; animproved expulsion circuit interrupter of the type discussed above thatshall utilize but a single arc passage, and that shall be provided withmeans for assuring the satisfactory interruption of both small and largecurrent arcs in that passage.

In carrying out this object of my invention, I provide a suitable meansfor defining an are passage, means, such as a fuse, for establishing anarc within that passage, and means of insulating material positionedwithin that passage so as to form a narrow passageway which issubstantially annular in cross-section. By this means, the opposedsurfaces of the insulating members which define the walls of the arcpassage are at all times spaced closely adjacent each other, and at thesame time the actual total crosssectional area or the arc passage iscomparatively large. Thus, even an are of low current magnitude iscaused to intimately contact the surfaces of the arc passage so as todecompose the gas evolving lining of that passage and effect itsextinguishment, and at the same time there is suilicient area whereinarcs or large current magnituale may spread so as to prevent thebuilding up of excessively high pressures Within the arc passage.

In the preferred embodiment of my invention, provide aicylindrical tubeof hard fibre vhaving relatively heavy side walls `i'or defining the arcpassage, and a cylindrical rod likewise of hard bre positioned withinand concentric with the y main tube. The arc passage is thus defined bya pair of concentric cylindrical surfaces and is periorce ofsubstantially constant width. Hard bre, as is well known in the art,decomposes when exposed to the heat of an electric arc to form a largequantity of an arc extinguishing gas, and during the operation of theinterrupter this gas flows longitudinally through the arc with anexpulsive action to effect its extinguishment.

It is, ofcourse, within the province of my invention that the outer tubeor the centrally disposed volume restricting member could be formed of arefractory material or of a gas evolving material different from thefibre. One material which I have found particularly suitable for this isboric acid, that material evolving a large quantity of an inorganic,non-inflammable gas when placed in proximity to an electric arc. Boricacid has another advantage in that thel surface does vnot becomeconducting even when heated to the temperature of an electric arc, thischaracteristic assuring that the full circuit voltage will not breakdown along the surface of the arc passage.

Since as pointed out above, one of the principal elds for immediateapplication of my invention is in connection with expulsion fuses, Ishall hereinafter describe an embodiment of' my invention as applied tosuch devices, without, however, in any way intending to restrict thescope of my invention except as indicated in the appende claims.

Referring to the single sheet of drawing,

Figure l is a sectional view of an expulsion fuse wherein are embodiedthe principal features of my invention;

Fig. 2 is a sectional view taken on the line II-II of Fig. 1;

Fig. 3 isa sectional view taken on the line III-HI of Fig. 1;

Fig. 4 is a bottom plan view of the fuse shown in Fig. 1; and

Fig. 5 is a fragmentary, sectional view showing a modified form of thefuse structure illustrated in the other figures of the drawing.

The expulsion fuse shown in the drawing comprises, generally, a maintube I of fibre or like insulating material which possesses sufncientstrength to withstand the pressures ordinarily developed within thesedevices, a metallic cap or ferrule 3 for enclosing the upper end of themain insulating tube, and a second ferrule 5, hraving a centrallydisposed opening 'I therein, for engaging the lower end of the maininsulating tube I. Both the upper and the lower ferrules are adapted tobe retained in position by means of suitable screw threads 9 formed inthe cooperating yportions of those members. A cylindrical rod member IIof insulating material, preferably nbre, is positioned within andconcentric with the main tube in order to define the annular arc passageIl.

The ,upper endof the rod member II is provided with a threaded openingIl therein which isadapted to be engaged by the positioning screw I1extending down through a suitable opening in the upper ferrule. lThelower end of the rod member Il is likewise provided with a threadedopening I9 which is adapted to be engaged by a sirnilar positioningscrew 2l extending through suitable opening in the bridge member 23which extends across the opening "i in the lower er- 'rule 5.

The central portion of the bridge member 23 is supported in the positionshown in the drawing, by means of a pair of radially extending spokemembers 25 formed integral with the lower ferrule. Except for thesespoke members 25, the opening I within the lower ferrule 5 is ofsubstantially the same cross-sectional area as the annular arc passageI3. The opening T has a funnel shaped portion 2l at its extreme lowerportion in order to facilitate the outflow of the arc extinguishing gasfrom the arc passage.

The cylindrical rod member II is provided with two sets of positioningmembers 29 which are shown particularly in Figs. 1 and 2. Thesepositioning members are adapted to project outwardly from the'rod memberI I in a substantially radial direction and are disposed between the rodmember and the main tube in order to prevent any warping which mightoccur during service from causing relative displacement of the rodmember II with respect to the inner walls of the main tube I. As shown,these positioning members 29 are formed of insulating material and arecemented or otherwise securely amxed to the outer surface of the rodmember II.' It is possible, however, to form these members of metal orany other material which will retain its strength during the arcextinguishing operation.

A fuse wire II, the upper end of which is connected by means of a screw33 to the upper ferrule l and the lower end of which is connected by-CTI adapted to be supported upon suitable clips or other means which arewell known to the art.

Inv the preferred embodiment of my invention,

the centrally disposed rod member II is formed of hard fibre as is themain tube I. This arrangement is desirable in that it is inexpensive,and at the same time provides an adequate blast of arc extinguishing gasfor effecting the extinguishment of the'arc. it is possible, and in somecases desirable, to form the rod member II of a refractory material, orthe main tube itself may be formed of a refractory material, and the rodmember formed of a gas evolving material. It is also possible. and insome cases desirable, to provide a lining l! of compressed boric acidfor the inner surface of the main tube I and to form the rod member IIof that material, such a structure being shown in Fig. v5. 'I'he use ofboric acid as a lining for the arc passage assures a gas blast which isnoninflammable and which is inorganic in lts chem-l ical composition.Also, the arc interrupting emciency ofl the gas evolved from a boricacid lining is somewhat greater than that evolved from a similar meansformed of nbre.

f Upon the occurrence of a predetermined overload in the circuitcontrolled by the device, the fusible element II melts and causes an arcto be established within the annular `irc passage Il. If the magnitudeof the overload current causing As mentioned above, however,v

rso

the melting of the fusible element Il is small, the arc occupies only aportion of the annular arc i'passage, but, because of the comparativenearness of the opposed surfaces which define this arc passage,asuiiiciently intimate contact between the arc and the gas evolvinglining is effected to assure a rapid extinction of the arc by theoutiiowing blast of gas which flows longitudinally through the arcpassage. If the magnitude of the arc current is large, a substantialportion of the annular arc passage may be occupied by the arc, and asthe upper range of safe operation of the device is reached, the entirearc passage will be entirely filled by the arc., Under any of thesecircumstances, however, the arc is caused to intimately contact the gasevolving lining of the arc passage walls and a rapid and efficientextinction thereof is effected.

From the foregoing, it will be seen that I have provided an improvedexpulsion-type circuit interrupter which is capable of satisfactorilyinterrupting arcs of small and of large current magnitude within asingle arc passage, this arrangement differing from the prior artdevices which utilize at least two arc passages for accomplishing thesame result. The structure of the preferred form of my invention iscomparatively simple and the cost of devices wherein my invention isembodied is not materially increased despite the greatly improvedoperation which results.

I have also disclosed certain preferred structural arrangements whichare particularly suitable for carrying out the objects of my invention,and I have disclosed certain types of materials which are particularlyadapted for use in conjunction with my invention.

While in accordance with the patent statutes, I have disclosed theforegoing details of practical embodiment of my invention, it is to beunderstood that many of these details are merely illustrative, and thatthe broad features of my invention are capable of much wider adaptationthan to the particular structure disclosed in this application. Idesire, therefore, that my invention shall be given the broadestreasonable construction, and that'the claims shall be limited only bywhat is expressly stated therein and by the prior art. y

I claim as my invention:

1. In an expulsionfuse, means of insulating material for defining theouter walls of an arc passage, said outer Walls completely enclosing thesides of said passage, means for closing one end of said passage duringeach circuit interrupting operation, the other end of said passage beingopen during each circuit interrupting operation, means including afusible element for establishing an aro within said passage, and meansof insulating material positioned within said passage for so restrictingthe volume of said passage that arcs of small current magnitude as wellas arcsof large current magnitude are caused to intimately contact theinner surface of said `wall defining means during each circuitinterrupting operation.

2. In an expulsion type circuit interrupter, means, at least partiallyof insulating material for defining a completely closed outer surface ofan arc passage; means for closing one end of said passage, the other endof said passage being open, during each circuit interrupting operation;meansat least partially of insulating material, positioned within saidpassage, at least during each circuit interrupting operation fordefining the inner surface of said arc passage; and means 3. In anexpulsion type circuit interrupter, l

means, at least partially of insulating material,V for defining acompletely closed outer surface of an arc passage; means for closing oneend of said passage, the other end of said passage being open, duringeach circuit interrupting operation; means, at least partially ofinsulating material, positioned within said passage, at least duringeach circuit interrupting operation for defining the inner surface ofsaid arc passage,

and means for establishing an arcrbetween said inner and said outersurfaces; said surface defining means so restricting the volume of saidpassage that arcs of small current magnitude as well as ares of largecurrent magnitude are caused to intimately contact the surfaces definingsaid arc passage during each circuit interrupting operation; at least aportion of one of the surfaces of said arc passage being lined with amaterial which is capable of evolving substantial quantities of an arcextinguishing gas when placed in proximity to an electric arc.

4. In an expulsion fuse, means defining the walls of a substantiallytubular passage which is completely closed along the sides thereof,means for closing one end of said passage at least during each circuitinterrupting operation, the other end of said passage being open duringeach circuit interrupting operation, means including a fusible elementfor establishing an arc within said passage, and means of insulatingmaterial for so restricting the volume of said passage that arcs ofsmall current magnitude as Well as arcs of large current'magnitude arecaused to intimately contact the inner surfaces of said passage duringeach (arc extinguishing operation, at least a portion of the innersurface of said wall defining means being lined with a material which iscapable of evolving substantial quantities of an arc extinguishing gaswhen placed in proximity to an electric arc. v

5. In a circuit interrupter for use with circuits subjected to overloadsof varying magnitude; means at least partially of insulating materialfor defining a completely closed outer surface of an arc passage; meansat least partially ofinsulating material positioned within saidpassageway, at least during each circuit opening cperation of saidinterrupter, for defining the inner surface of said arc passage; andmeans for establishing the arc incident to each opening op- 60 rentmagnitude are caused to intimately contact the surfaces defining saidarc passage during the circuit interrupting operation; at least aportion of one of said surface defining members being formed of amaterial which is capable of evolving an arc extinguishing gas whenplaced in proximity to an electric arc and means for venting saidpassage.

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6. In a circuit interrupter for use with circuits subjected to overloadsof varying magnitude; means at least partially of insulating materialfor defining the outer surface of an arc passage; means which is also atleast partially of insulating material and which has a substantiallycylindrical outer surface positioned within said passageway, at leastduring each arc extinguishing operation of said interrupter, fordefining the inner surface of said arc passage; one end of said passagebeing open at least during the circuit opening operation; said outer andinner surface defining means being completely closed, means forestablishing the arc incident to the opening operation of saidinterrupter within said a-rc passage; .the'cross sectional area of saidsurface defining means which is positioned within said passageway beingso correlated with respect to the cross sectional area of saidpassageway that arcs of small current magnitude as well as arcs of large-current magnitude are caused to intimately contact said inner and saidouter surfaces during each circuit interrupting operation.

'7. In a circuit interrupter for use with circuits subjected tooverloads of widely varying magnitude; means at least partially ofinsulating material for defining the outer surface of a substantiallycylindricalarc passage; 'at least a portion of said outer surface beingformed of a s lid material which is capable of evolving an arcextinguishing gas when placed in proximity to an electric arc; meansalso at least partially of insulating material and which has asubstantially cylindrical outer surface disposed within andsubstantially concentric with said passageway, at least during each arcextinguishing operation of said interrupter, for defining the innersurface of said arc passage; said passage being open at one end at leastduring the circuit interrupting operation; but otherwise completelyclosed, and means for establishing the arc incident to each openingoperation of said interrupter within said arc passage; the arrangementof said outer and said inner surfaces dening means causing said arcpassage to have the, substantial form of a hollow cylinder, the crosssectional area of said means positioned within said passageway being socorrelated with respect to the cross sectional area of said passagewaythat arcs of small current magnitude as well as arcs'of large currentmagnitude are caused to intimately contact said surfaces which definesaid armpassageY during the operation of said interrupter. g Y

8; In a circuit interrupter; hollow means which is formed at leastpartially of insulating material for defining the walls and the outersurface of an arc passage having a length at least several times itsgreatest width; rod means which is also at least partially of insulatingmaterial positioned within said hollow wall defining means, at leastduring each opening operation of said interrupter for defining the innersurface.

of said arc passage; said outer and said inner surface defining meansbeing so formed that said arc passage has the substantial form ofafhollow prism completely closed on its sides; and means forestablishing the arc incident to each circuit opening operation of saidinterrupter within said arc passage; at least a portion of said surfacedefining means being formed of a material which iscapable of evolving anarc extinguishing gas when placed in proximity to an electric arc; thephysical dimensions of said rod means lbeing so alessio correlated withrespect to the physical dimensions of said Wall defining means that arcsof small current magnitude as well as arcs of large current magnitudeare caused to intimately contact the surfaces defining said arc passage.

9. In an expulsion fuse; means of insulating material for defining thewalls of and the outer surface of an arc passage having a length whichis at least several times its greatest width; means for closing one endof said arc passage, at least during each circuit opening operation, theother end of said arc passage being open, at least during each circuitopening operation; rod means of insulating material positioned withinsaid arc passage, at least during each circuit opening operation,fordefining the inner surface thereof; and fusible means forestablishing the arc incident to each opening operation of said fusewithin said arc passage; the opposed surfaces which define said arcpassage being completely closed and at least a portion thereof beingformed of a material which is capable of evolving an arc extinguishinggas when placed in proximity to an electric arc; the physical dimensionsof said rod means being so correlated with respect to said wall definingmeans that said arc passage has the substantial form of a hollow prism,the thickness of which is such that arcs of small current magnitude aswell as arcs of large current magnitude are caused to intimately contactthe opposed, defining surfaces thereof.

10. In an expulsion fuse; means of insulating material for defining thewalls of a substantially cylindrical passageway; means for closing oneend of said passage, at least during each circuit opening operation, theother end of said passage being open, at least during each circuitopening operation; a substantially cylindrical rod adapted to bedisposed within and substantially concentric with said passageway, atleast during each opening operation of said fuse for defining the innersurface of a space wherein the arc incident to the opening operation ofsaid fuse is established; and means including a fusible element forestablishing said arc within said space; the opposed surfaces whichdefine the space wherein said arc is established being completely`closed and at least a portion thereof being formed of a material whichis capable of evolving an arc extinguishing gas when placed in proximityto an electric arc; the cross sectional area of said rod means being socorrelated with respect to the cross sectional area of said cylindricalpassage formed within said wall dening means that arcs of small currentmagnitude as well as. arcs of large current magnitude are caused tointimately contact said opposed surfaces during the operation of saidfuse.

11. In a circuit interrupter, means at least partially of insulatingmaterial for defining the outer surface of an arc passage, means forclosing one end of said passage, the other end of said passage beingopen at least during each circuit opening operation, means at leastpartially of insulating material positioned within said passage at leastduring each circuit interrupting operation for defining the innersurface current magnitudeas well asV arcs of -large current magnitudeare caused to intimately contact the surfaces dening the arc passageduring the circuit interrupting operation, said passage having agenerally annular cross-section to enable lateral movement of the arctherearound.

l2. In a circuit interrupter, means at least partially of insulatingmaterial for defining the walls of a tubular arc passage, said passagebeing completely closed along itslsides and open at one end at leastduring the circuit interrupting operation, means for establishing an arclongitudinally of said passage, said passage having a generally annularcross-section to enable lateral movement of the arc therearound, saidwall defining means restricting the volume of said passage so that arcsof small current magnitude as well as arcs of larg'e current magnitudeare caused to intimately contact the surfaces delining said arc passageduring each circuit interrupting operation. A

13. In a circuit interrupter, means at least partially of insulatingmaterial for defining the walls of a tubular arc passage, the wallsdefining said passage being completely closed and having at least aportion thereof lined with a material which gives off a gas when actedupon by an arc to aid in extinguishing the arc, means for venting saidpassage, means for establishing an arc longitudinally of said passage,said passage having a generally annular cross-section to enable lateralmovement of the are therearound, the width of said passage beingrestricted so that arcs of small current magnitude as well as arcs oflarge current magnitude are caused to intimately contact the wallsdefining said arc passage during each circuit interrupting operation.

14. In a circuit interrupter, means at least partially of insulatingmaterial for defining the outer surface of an arc passage, means forclos- `ing one end of said passage, the other end of said passage beingopen at least during each circuit opening operation, means at leastpartially of insulating material positioned within said passage at leastduring each circuit interruption for defining the inner surface of saidarc passage, means for holding said last-named means against lateraldeflection within said passage and means for establishing an arc betweensaid inner and said outer surface, said surface defining means sorestricting the volume of said passage that arcs of small currentmagnitude as well as arcs of large current magnitude are caused tointimately contact the surfaces defining the arc passage during thecircuit interrupting operation.

15. In a circuit interrupter, a tubular member at least partially ofinsulating material for defining the outer surface of an arc passage,means for closing one end of said passage, the other end of said passagebeing open at least during each circuit opening operation, a cylindricalmember at least partially of insulating material positioned within saidpassage for dening the inner surface thereof, means disposed betweensaid tubular member and said cylindrical member for holding the latteragainst lateral displacement and means for establishing an arclongitudinally of said passage, said passage having a generally annularcross-section to enable lateral movement of the arc therearound.

16. In a circuit interrupter, a tubular member at least partially ofinsulating material for delining the outer surface of anarc passage,means for closing one end of said passage, the other v end of saidpassage being open at least during each circuit opening operation, acylindrical member at least partially of insulating material positionedwithin said passage for defining the inner surface thereof, spacingmeans disposed between said tubular member and said cylindrical memberintermediate the. ends thereof for preventing lateral movement of saidcylindrical member within s aid passage, and fusible means forestablishing an arc longitudinal of said passage, said passage having agenerally annular cross-section to enable lateral movement of the aretherearound, the width of said passage being restricted so that the arcsof small current magnitude as well as arcs of large current magnitudeare caused to intimately contact the walls defining said arc passageduring each circuit interrupting operation.

17. An expulsion fuse comprising a hollow tube of insulating material,conducting terminals affixed to said tube adjacent the ends thereof, acylindrical element of insulating material having an outside diameterless than the inside diameter of said tube supported between saidterminals Within said tube, spacing members disposed between said tubeand said element intermediate the ends thereof for holding said elementagainst lateral displacement within the tube and a fusible link withinsaid tube connected at its ends to said conducting terminals, said tubebeing closed at one end and having vent openings at the other end topermit the expulsion of the products of decomposition resulting from theoperation of said fusible link.

18. An expulsion fuse comprising a hollow tube of insulating material,terminal members releasably attached to the respective ends of saidtube, a cylindrical element of insulating material having an outsidediameter less than the inside diameter of said tube disposed within thetube and supported between said terminal members to provide an arcpassage of generally annular crosssection, support members disposedbetween said tube and said cylindrical element intermediate their endsfor holding said element against lateral displacement within said tubeand a fusible ele,- ment within said tube connected between saidterminal members for establishing an arc within said passage, saidpassage being closed at one end by one of said terminal members andvented at the other end through openings in the other of said terminalmembers.

19. In a circuit interrupter, a tubular member at least partially ofinsulating material for defining the outer surface of an arc passage,means for closing one end of said passage, the other end of said passagebeing open at least during each circuit opening operation, a cylindricalmember of compressed boric acid positioned within said passage fordefining the inner surface thereof, and means for establishing an arclongitudinally of said passage, said wall defining means restrictlng thevolume of said passage so that arcs of small current magnitude as wellas arcs of large current magnitude are caused to intimately contact thesurfaces defining said arc passage during each circuit interruptingoperation.

CLINTON L. DENAULT.

